High vacuum television tube



P 1933- K. SCHLESINGER 2,131,192

HIGH VACUUM TELEVISION TUBE Filed May 4, 1935 2 Sheets-Sheet 1 Mia/M.

Sept. 27, 1938.

K. SCHLESINGER 2,131,192

HIGH VACUUM TELEVISION TUBE Filed May 4, 1955 2 Sheets-Sheet 2 PatentedSept. 27, 1938 UNITED STATES 2,131,192 r HIGH VACUUM TELEVISION TUBEKurt Schlesinger, Berlin, Germany, assignor to RadioaktiengesellschaftD. S. Loewe, Berlin- Steglitz, Germany Application May 4, 1935, SerialNo, 19,817 In Germany May a, 1934 Claims.

The present invention relates to a Braun tube for television purposeswhich is preferably operated in a highly evacuated condition, in whichelectro-static fields are employed throughout for 5 producing anddeflecting the image point, and in which all of the electrodes by meansof which the fields are produced aregarranged within the tube, so thatthe tube is at once in an operable condition without further externalauxiliary devices, such as coils and the like.

The tube according to the invention, an embodiment of which isillustrated by way of example in Fig. 1, may, broadly speaking from thepoint of view of physics, be divided into three parts: first, the beamcondensing device (condenser" in an optical sense) with control grid andperforated diaphragm, secondly the reproducing lens with tubular. memberup to the anode, and thirdly two deflecting condensers.

The indirectly heated cathode consists of a small nickel hood I, whichat its front end, the diameter of which is 2 mm., is ground completelyfiat and is furnished with a small recess 2 of .1 mm. only in depth,which is filled up with a highly emissive substance, for example amixture of earth alkaline oxides, such as are well known in the art. Inselecting the size of the recess 2 the size of the picture and thenumber of scanning lines are to be taken into consideration; the exactcalculation of the size of the em ssive layer will be set forth below.The glow hood 2 is heated by means of a preferably slotted spiral 3arranged in the interior of the hood, which may be insulated from 2 by asmall insulating tube (not shown) consisting for example of magnesia.The complete cathode is located exactly in axial position within acontrol cylinder 4 by the use of a cylindrical fitting, so that theemissive surface is exactly aligned with the tube axis. 40 The cylinder4, in turn, is fitted by means of two stamped collars 5 and 6 ontocertain elementsfor example glass rodsprovided for centering the wholeof the tube system in itself, and carries at a small distance from itsupper end a dia- 45 phragm 1 having a narrow aperture, which diaphragmis disposed in close neighbourhood of the glow head I, for example at adistance of within .5 mm. therefrom. The cylinder extends beyond thegrid diaphragm I by a definite amount 8 (see below).

The cathode ray proceeding from 2 and controlled in its intensity by Iis preliminarily concentrated by 8 and impinges on a narrow diaphragmaperture 9 of approximately the same size as the emissive surface 2. Thediaphragm plate carrying the aperture 9 consists of a completelyoutgassed metal having a high fusing point, for example molybdenum,which preferably is welded on to a bronze supporting plate Hi to formthe diaphragm proper. The supporting plate Ill possesses a considerablywider aperture, so that the same is not touched by the directlyimpinging cathode ray and a local heating of the bronze plate isprevented. In this way the danger of subsequent discharge of gas withinthe tube is eliminated.

The aperture in the perforated diaphragm 9 onto which the cathode ray isprojected with varying intensity is reproduced by an electron opticalsystem on the screen, viz, by the electrode system comprising electrodesll, l2, l3 and It. The main purpose of tubular member I I (bronze)consists in screening the cathode ray traversing the interior thereofagainst external electrostatic fields. The length which this member isto be given may be readily calculated from the desired scale ofenlargement of the reproduction with a given constructional length ofthe tube (see below). The tubular member H is linked up with a lowerpositive bias than the main anode l4 and preferably than the diaphragmit) also. The path of the cathode ray does not undergo anyelectronoptical refraction within the tubular member, since inaccordance with the invention the diameter of the tubular member isselected to be large as compared with the diaphragm aperture 9. It istrue that the applicant has been able to ascertain definitely that awide tubular member of this kind which is biased negatively in relationto the rays is ineffective in practice only as regards rays in thevicinity of the axis, i. e., the main bundle of rays, whilst as regardssuch marginal ray as stray to an appreciable extent it effects anauxiliary concentration which is very helpful for a satisfactoryoperation of the tube. It is possible, for example, to completelysuppress by a bias of this kind of the tubular member in relation to thediaphragm the known halation eifects, which otherwise will appear on theluminous screen.

By means of an intermediate diaphragm with large aperture l2 and a shorttubular extension l3 in coniunction'with the double anode l4 situated infront of the tubular member the cathode ray refraction proper isproduced. The peculiar form of the electrodes is the result ofsystematic investigations of electron-optical lenses. The problem whichhas been solved in this respect consisted in the first place inproducing by electrical design and adjustment the effect of aspherically corrected lens having for the marginal rays the same focaldistance as for the central rays. Secondly no refraction should be exerted on the electrons after leaving the main anode l4, and thirdly itshould be possible to provide deflecting plates behind the anode withoutthe symmetry of rotation of the lens being lost. (Behind means: moreremote from the cathode than.)

The lens l2, l3, I4 as shown satisfies these reby means of two platesi6, i! in the horizontal means 26, are fully suflicient. The one oi thetwo mediate diaphragm l2 quirements as soon as the correct difference inpotential has been adjusted between I! and i4, it being maintainedelectron optical refraction, is performed by means of a potentiometer I6 which is connected with the terminal l5, and is connected betweentheearth potential, which is simultaneously linked up with the diaphragml0 and the anode I4, and the potential oi the cathode. The refractiveiield is ited to the lens space (i. e., the space between the electrodesproducing the lens) by virtue oi the screened construction of the lenselectrodes both towards the front as well as towards the rear. The

apertures may preferably be made not larger than the largestcross-section of the electron bundle.

The spherical correction of the lens is obtained 1 only uponintroduction of the rear intermediate diaphragm i2 into the tubularmember. lithe width of this diaphragm i2 is made approximatelyj as largeas'the tubular extension it, the potential levels have substantially theform of an inscribed spherical surface,and the lens acts as aspherically corrected one, which is not trueii the interis omitted. Itmay be added that the diaphragm l2 acts at the same time as a select onpupil by which those marginal rays are stoppedwhich divergetoo strongly.

The third requirement, viz, the? independency.

oi" the symmetry of the lens field from thefle1ds of thedeflectingplates arranged behind the anode I4, is obtained by-increasingthe axial length of the anode to a certain extent by a small tube i5.

plates arranged behind the anode ll into e lens In this manner thepenetration of the ileljizpf the fleld is greatly reduced, and it is infact produced by the use oi a circular diaphragm 9, is an undisturbedround point. g, v The deflection of the cathode rays takes placedirection, and l8. IS in the vertical direction. The

deflection is unavoidably associated with simul,-,

taneous 1 disturbances in the sharpness oi the image point at the edgeofthe image it, as heretofore usual, the one plate being connected withthe deflecting voltage generator, the other plate is earthed.

In accordance with the invention. it is possible to overcome thisdifliculty, which heretofore has prevented the construction of tubesoperating with purely electrostatic means, by, operating the two platesin reverse phase with respect to each other. For this purpose there isprovided a special relaxation oscillation apparatus, for example asshown, of the twin circuit including a twin tube 20. ent grid-anodesystems 22, 23 and, 28 are arranged about a common cathode. Simplesingle grid systems with a reciprocalnoi approximately 2% incombinationwith a;mica disc screening systems, for example, the lower one, isconnected directly with the is charged through the medium 01' theresistance 21, and discharged through the medium of a gas? filledgrid-controlleddischarge device 29,01 that general type. a well knownrepresentative of which. is the tube called "'Ihyratron (registeredtrade-H mark). The anode 25 of the system here in question is connectedwith a working resistance 20 of approximately 100,000ohms, and with theone dcfleeting plate I1 01' the televisiontubethrough the medium of acoupling condenser 3| In order now to obtain for the other deflectingplate It an equal positive. in relation to II, This adjustment, whichdetermines the degree. oi

accomplished that the stationary image point, whichis which consists,amplifier tube Two independ relaxation condenser 20, which potential ofopposite phase the plate leakage resistance 32 (not exceeding 100,000ohms) is connected; with the second control, grid 221-oi the upperr'systemof the twin. amplifier tube 20, the

relaxation potential being reduced by means of a 6 tapping 32', exactlyto the extentto which the 3 same has been amplified in the lower half ofthe ,tube 24, 25 (amplification factorl/D). There is accordinglyobtainedat the working resistance 33 of; thesecond; anode 22 the desiredreverse relaxation potential havingthe same amplitude but reverse phase.This reverse potential is conducted to the second deflecting plate It ofthe television tube through the medium of a second coupling condenser;this deflecting plate being also earthed through a leakage resistance 34larger than 32.

By meansof a similarrelaxation arrangement likewise comprising acountercadence amplifier the front pair of deflecting plates l8, i9 isalso operated in reverse phase. It mustbe particu-., larly emphasizedthat without such. reverse phase circuit the problem does not appearcapable of solution. The errorswhich then occur, 1. e., in the case oithe usual single phase operation are lack of sharpness atthe, edge byvariation 01' the focal distance, and a trapezoidal shape of thepicture. These errors inthe image are all avoided byfreverse phaseoperation of the two deflecting plates. It is true that the mutualapproach of the pairs of plates, towards. each other and the anodeshould not be driven farther than to within two to three times the widthoimouth (distance between, the rear edges, directed towards the cathode,of the plates of a pair of deflecting plates).

Improvements in "theoperation at the plates. may be obtained by givingthem a suitable shape.

It is convenient to disposethem ina tilted position in relation to eachother, asa certain gain in their specific sensitivity (deflection in mm.per volt) is thereby obtained. Beyond this the sensitivity of thedeflection is, with the use of a reverse phase circuit, twice as greatas with a. usual circuit, 1, e., the anode battery potential 35,,may behalt asgreat as usually, which is of particular advantagein the case ofshort-ray high-vacuum tubes in which the; deflecting plates require tobe approached as near as possible towards the screen. It has been foundthat to avoid interfering displacement of the ray owing to wall chargesa silver coating 36 should be provided, which may preferably beconnected with earth,i. e., with the anode I 4 or diaphragm III.; Theapplicant has ascertained, however, that this'silvercoating requires tocover merely a part of the bulb, viz, it

requires to extend only iromthe anode it up to the front plates i8, i9,which already project into the interior'oi the bulb. Equally asimportantas this screening is an outermagnetic screening oi the tube by means 01an iron shield 31, which needs only to consist of ,a sheet ofapproximately 1 mm. thickness having a good magnetical conductivity,which, however, must be closed in annu-, lar form (welded or drawn) ,andneed merely extend from the hot cathode to the anode.

The shield is preferably, likewise connected with i earth. It isonlywith the provision of this shield that it is possible to operate thetube in any desired position in relationg t o the magnetic earth field,so thatparticular potentiometers for adjusting the position of thecentre oithe image are unnecessary.

. lack ofsensitivenessagainst field disturbances is favoured bytheextensive preliminary acceleration of the ray which iseilected accord- 7ing to the invention by the high positive potential of the diaphragm 9.

The light intensity and function of the whole tube is essentiallydetermined by the path of the rays between cathode and diaphragm. Therays should be suitably influenced in this particular region, 1. e., insuch manner that as far as possible all electrons in the first place arepassed through the narrow aperture, and secondly continue to move insuch a narrow cone that no stopping-of electrons occurs later neither inthe lens nor in the diaphragm and that all electrons reach the screen inone definite image point. The better the form of the bundle obtained,the more sensitive the deflection may be made, as a. bundle having asmall cross section in the plate field practically is not subject todisturbances even in highly sensitivev plate systems, whilst a bundlehaving a large cross section in the region in question undergoes lateraldistortions in such systems.

The applicant has found that the simple condensing lens I, 8, III asshown, which exactly corresponds in its operation with the main lens l2,l3, I4, is capable of fulfilling the stated requirements, but merelyunder the condition that the free length of the ray between cathode anddiaphragm is not too small. The applicant has found that the spacingl/lll must amount to at least 10 mm. This spacing is calculated inpractice by use of the simple diopter law on the basis of the requiredwidth of bundle. One may in fact obtain a survey on the conditions ofray propagation as influenced by the condensing lens by drawing the mostunfavourable rays from edge of the cathode spot over the edge of the diphragm aperture. These rays must then undergo such a,

refraction in the condensing lenses as to pass through the imageproducing lens and through the space between the deflecting plates.

With a large spacing 'I/ III as stated above and the cylinder extension8 necessary for spherically correcting the condensing lens, whichextension fills out approximately one-half of the spacing. it is clearthat the anode fleldattracting the electrons is rather weakened. If onlyfor this reason alone the separate and sumciently strong positive biasof the diaphragm I0 is essential if it is desired to obtain brightimages. In particular cases it may be necessary to provide a screeninggrid diaphragm 38 together with a particular intermediate cylinder 39,in order to be able to make the requirement for suitably guiding of theray unobstructedly consistent with the requirement for sufiicient anodicstrength of field as is necessary for producing cathode rays of greatintensity.

In the following it will be set forth in what manner a tube according tothe invention may be dimensioned in practice.

Diameter of aperture in diaphragm for 180- line picture size 17x20 mm .5

Form of aperture is reproduced sharply; therefore also square orhexagonal apertures may be used.

Current utilizationggg: m} giggfifigg Length of tubular member IIapproximately mm 100 Diameter of aperture of lens ll, l2 mm 7 Tubularmember extension 13 mm 7 Diameter of tubular member mm 20 Spacingbetween edge of tubular member and anode mm 7 Diameter of anode tube I5mm 7 Length of anode tube l5"; mm 7 Space between anode l5 and edge ofrear deflecting plate mm 10 Width of mouth of rear deflecting platessystem mm 6 and 15 Length of rear deflecting plates mm 35 Width of mouthof front deflecting plates system mm 6 and 20 Distance between rearplates system and front plates system mm 20 Spacing between anode I5 andluminous screen mm 250 Anode potential volts 2,000 Maximum powerrequired watt 1 Heating 4 volts, A. C. or D. C amp .4 Potential oftubular member, volts variable,

approx 1,500

lation generator 35 volts 800 It is to be understood that the above dataonly refer to a particular form of embodiment of the tube according tothe invention, to which the invention is in no way limited.

The individual parts of the system may be mounted on the base of thetube and centered in relation to each other preferably by the use ofinsulating supporting means, which may preferably consist of glass. Theindividual current leads are preferably all taken to a socket secured tothe base of the tube. The current supply to the metallic coating 36 ispreferably efiected so as to avoid special fusing-in points by means ofsprings fixed to the electrode system and conductively connected forexample with the anode. These springs may at the same time serve forsupporting or guiding the system within the neck of the tube. For thispurpose they may be constructed for example in the form of comparativelystrong, bent blade springs.

A practical and convenient technical form of embodiment of the tubeaccording to the invention is illustrated by way of example in Fig. 2,like references being given to like parts in the two figures.

I claim:

1. A Braun tube more particularly for television purposes comprisingmeans including a cathode disposed near one end of the tube forproducing a cathode ray, an image screen disposed at the end of the tubeopposite to that end near which said cathode is disposed, and anelectron-optical lens system for projecting the cathode ray onto saidimage screen in the form of a sharply defined image point, saidelectron-optical lens system comprising a tubular member having its axisdisposed in the direction from said cathode to said screen and having adiameter which is considerably larger than the diameter which thecathode ray possesses when travelling through said tubular member, anapertured disc shaped sion purposes comprising means including a cathodedisposed .near one end of. the tube for producing a cathode ray, animage screen dis posed at the end of the-tube opposite to that end nearwhich said cathode is disposed, and an electron-optical lens systemfortmfflicting the cathode my: onto said image screen in the form of asharply defined image point, said electronoptical lens system comprisinga tubular member having its axis disposedin the direction from saidcathode to said screen and having a diameter which is considerablylargerthan the diameter which the cathode ray possesses when travellingthrough said tubular member, an anode mounted near said tubular memberbetween said tubular member and said image screen, said anode comprisingat its side facing said tubularmemher an apertured plate shaped portiondisposed perpendicularly to the axis of said tubular member, said anodehaving a tube-like extension in the direction away from said tubularmember. and an apertured d aphragm separating said tubular member intotwo parts and being mounted near that edgeof said tubularmember facingsaid anode, said anode being adapted to be supplied with a h gh positivepotential in relation to said cathode. said tubularmemberbe ing adaptedto be supplied with apotential positive in relationto said cathodebutnegative in relation to said anode. l

3. A Braun tube more particularly for television purposescomprisingmeans for producing a cathode ray, means to produce difierent electricfields for influencing the cathode ray in different axially consecutivezones of the tube; an image screen disposed at one end of the tube to behit by the cathode ray after the cathoderay has passed through thementionedaxially consecu tive zones, an electrode system located in aspace of the Braun tube, both at the sides of which space facing saidscreen and facing away from said screen at least one of said fields islocated, said electrode system comprising electrodes adapted to producean electron-optically refractive field, and to at the same time screen.this refractive held against the fields at the side of said electrodesystem facing said screen as well as at the side of said electrodesystem facing away from said screen, said electrode system comprising atubular member having its axis directed towards said screen and having adiameter which is considerably larger than the diameter which thecathode ray possesses when travelling through said tubular member, anapertured disc shaped anode mounted perpendicularly tothe axis of saidtubular member near said tubular member between said tubular memberandsaid image screen, and an apertured diaphragm separating said tubularmember into two parts ,and

being mounted near that edge of said tubular edge of saidtubular member.

ducing a cathode ray,

said anode being high positive potential in relation to said cathode,said tubular member being adapted to besupplied with a potentialpositiveiin relation to said cathode but negative in relation to saidanode.:

4. A Braun tube more particularly fortelevision purposes comprisingmeans including a cathode disposed near one end of the tube for proanimage screen disposed atthe end of the tube opposite to that end nearwhichsaid cathode is disposed, and an electronoptical lens system forprojecting the cathode ray onto said image screen in. theform of asharply defined image point, said electronvoptical lens systemcomprising a tubular member having its axis disposed in the directionfrom said cathode to said screen and having a diameter which is,considerably larger thanthe diameter which the cathode ray possesseswhen travelling through said tubular member, an apertured disc-shaped,anode mounted perpendicularly to the axis of. said tubular member nearsaidtubular member between said tubular memberandsaid jmage screen, andan apertured diaphragm separating near that edge of said tubular membersion purposes comprising means including a oathode disposed near one endof J the tube for producing a cathode ray, an image screen disposed atthe end of the tube opposite to' that end near which said cathode isdisposed,and an electronoptical lens system for projecting'the cathoderay onto said image screen in the form of a sharply defined image,point, said electron-op this! lens system comprising; a tubular memberhaving its axis disposed in the direction from said cathode to saidscreen and having a diameter which is considerably largerthan thediameter which the cathode ray possesseswhen traveling through saidtubular member, anapertured disc shaped anode mounted perpendicularly tothe axis of said tubular member near said tubular member between saidtubular member andsaid image screen, and an apertured diaphragmseparating said tubular member into two parts and beingzmounted nearthat edge of said tubular; member facing said anode, both said anode andsaid apertured diaphragm having apertures the cross-sectionsof which aresubstantially equal to the cross-sections which the cathode ray has inthe respective planes of said apertures, the

distance of said apertured diaphragm. from the edge of said tubularmember facing said anode being approximately equalto the diameter of theaperture in said apertured diaphragm, said anode being adapted to besupplied with a high positive potential in relation to said cathode,said tubularmember being adapted tobe supplied with a potential positivein relation to saidcathode but negativein relation to said anode.

KURT SCHLESINGER.

